The findings — some in animals, some in people — suggest that people may be making a mistake if they're relying primarily on crossword puzzles and brain-training games for mental wellness.

"We definitely have more evidence for exercise," said Teresa Liu-Ambrose of the University of British Columbia. Liu-Ambrose moderated a panel of scientists who presented studies showing that physical activity offers a wide range of brain benefits.

In a study of rats, those that ran on a treadmill for at least four months scored higher on memory tests as they got older, said Yong Tang of Chongqing Medical University in Chongqing China. The running rats also had more blood vessels and white matter in their brains than did sedentary rats. He said the message for people is clear: "Exercise no matter how old you are."

Exercise also helped rats reverse the Parkinson-like slowing of movement that often come with age. The condition, called bradykinesia, affects more than half of people who live to be 85 or more and is responsible for many falls.

But with elderly rats, 12 consecutive days of using a treadmill greatly improved their mobility, said Jennifer Arnold of Louisiana State University. The benefit may come because exercise is raising levels of dopamine, a brain chemical that is important for movement, Arnold said.

Finally, a pilot study of a dozen young adults in Australia found that exercise relieves depression, said Robin Callister of the University of Newcastle. All of the participants, aged 15 to 25, had been diagnosed with major depressive disorder. But after 12 weeks of exercise, 10 of them were no longer categorized as depressed, Callister said.

One reason exercise provides mental benefits may be that it actually requires the brain to do a lot of work, Callister said. Even going on a run means the brain is coordinating complex movements, she said. And team sports or group exercises also activate parts of the brain devoted to social interactions.

"I think people underestimate how much the brain is involved in physical activity," Callister said.